The present invention relates to systems and methods for controlling a powertrain including a lean burn/DISI engine and automatic transmission relative to ratio changing and NOx purging cycles.
As known, lean burn internal combustion engines including direct injection, spark ignition (DISI) engines may be operated in various modes lean of stoichiometry where the pumping losses are reduced and the thermodynamic efficiency of the engine is increased. Lean burn/DISI engine technology provides for lean combustion which may result in significant fuel economy improvements. Catalysts, such as three-way catalysts or NOx traps, are used which absorb NOx when lean. These catalysts are periodically purged by operating rich of stoichiometry for a short duration. During cruise control and light acceleration operation, a 30-45 second lean operation cycle may be followed by a 2-3 second purge cycle, for example. During a NOx purge cycle, throttle, spark, and fuel are controlled to maintain a relatively constant engine torque to minimize any effect on vehicle performance or driveability.
For automatic transmission applications, transmission ratio changes, including gear shifts and torque converter clutch applies/releases, may be greatly affected by unpredicted or uncontrolled changes in engine torque. In addition, consistent transmission shift quality may require engine torque modulation during a ratio change. To properly control engine torque to maintain consistent shift quality, it is desirable to coordinate control of air/fuel ratio changes in the DISI engine, such as those that occur during NOx purge cycles, with shift scheduling of the automatic transmission.
An object of the present invention is to provide a system and method for synchronizing or coordinating control of a DISI engine and automatic transmission.
In carrying out the above object and other objects, advantages, and features of the present invention, a system and method for controlling a powertrain having an automatic transmission and an internal combustion engine capable of operation in at least lean burn and stoichiometric modes include determining a current operating mode for the engine, determining a next operating mode for the engine, and delaying a requested transmission ratio change if the ratio change can not be substantially completed before transitioning from the current operating mode to the next operating mode.
The present invention provides a number of advantages. For example, the present invention reduces or eliminates driveability related issues associated with interaction of an air/fuel transition of a lean burn/DISI engine and ratio change of an automatic transmission, such as occurs during periodic NOx purge cycles, for example. The present invention provides consistent and predictable gear shift quality through appropriate coordinated scheduling of ratio changes and operating modes of a DISI/lean burn engine.
The above advantages and other advantages, objects, and features of the present invention, will be readily apparent from the following detailed description of the best mode for carrying out the invention when taken in connection with the accompanying drawings.